According to an article in “Medicine & Science in Sports & Exercise” research data suggest that endurance athletes are at an increased risk for upper respiratory tract infection (URTI) during periods of heavy training and the 1- to 2-wk period after race events. The risk appears to be especially high during the time following marathon-type race events. Moderate physical activity may reduce URTI, but among runners varying widely in training habits, the risk for URTI is slightly elevated for the highest distance runners. Clinical data support the concept that heavy exertion increases the athlete’s risk of URTI because of negative changes in immune function and elevation of the stress hormones, epinephrine, and cortisol. On the other hand, there is growing evidence that moderate amounts of exercise may decrease the risk of URTI through favorable changes in immune function without the negative effects of the stress hormones.
So what’s an athlete to do? Endurance athletes are often uncertain whether they should exercise or rest when they have an infection, and there is little data available to provide definitive answers. Most clinical authorities in this area recommend that, if the athlete has symptoms of a common cold, then regular training may be safely resumed a few days after the symptoms have subsided. However, if there are symptoms or signs of systemic involvement – for example, fever, extreme tiredness, muscle aches, swollen lymph glands – intensive training should not be resumed for 2-4 weeks.
Medicine & Science in Sports & Exercise: “Is infection risk linked to exercise workload?” July 2000 – Volume 32 – Issue 7 – pp S406-S411
“Exercise, upper respiratory tract infection, and the immune system”., Department of Health and Exercise Science, Appalachian State University, Boone, NC 28608.